In this case you will need to create a new stored procedure to be able to get what you are looking for. The option of changing the XML file is not vailid because the only thing that the XML file does is send the require variables to the stored procedure.
Currently the xml will allow me to push the interval value (30/60/all). Can't i just modify the xml to push a new value (15) to the same sp?
I've done this for lots of customers. If there is an 'interval' parameter, then it can be customised to whatever you want by editing the XML on the client PC.
The SQL procedure at the back end just takes an Integer, so it can be anything from 1 to whatever.
This is the XML file in the templates directory in the install folder. The only drawback is that there's no way to push this out automatically to all clients (well, not driven by Cisco etc - obviously there are a million ways to do this)